Coated article with low-E coating having zinc stannate based layer between IR reflecting layers for reduced mottling and corresponding method

ABSTRACT

A coated article is provided which may be heat treated (e.g., thermally tempered) and/or heat bent in certain example instances. In certain example embodiments, a zinc stannate based layer is provided between a tin oxide based layer and a silicon nitride based layer, and this has been found to significantly reduce undesirable mottling damage upon heat treatment/bending. This results in significantly improved bendability of the coated article in applications such as vehicle windshields and the like.

This invention relates to a coated article including a low-E coating. Incertain example embodiments, the coated article may be heat treated(e.g., thermally tempered, heat bent and/or heat strengthened). Incertain example embodiments of this invention, the coated articleincludes a zinc stannate based layer provided over a tin oxide basedlayer, in a central portion of the layer stack between first and secondIR reflecting layers (e.g., Ag based layers). In certain exampleembodiments, the zinc stannate based layer is provided between andcontacting the tin oxide based layer and a silicon nitride and/orsilicon oxynitride based layer, so that the layer stack between the IRreflecting layers moving away from the glass substrate comprises layerscomprising the following materials: glass . . . Ag . . . SnO/ZnSnO/SiN .. . Ag . . . . It has surprisingly been found that this layer stackportion significantly reduces mottling problems upon heat treatment,thereby resulting in a more durable coated article. Coated articlesaccording to certain example embodiments of this invention may be usedin the context of vehicle windshields (e.g., in laminated form),insulating glass (IG) window units, other types of windows, or in anyother suitable application.

BACKGROUND OF THE INVENTION

Coated articles are known in the art for use in window application suchas vehicle windshields, insulating glass (IG) window units, monolithicvehicle windows, and/or the like. It is known that in certain instances,it is desirable to heat treat (e.g., thermally temper, heat bend and/orheat strengthen) such coated articles for purposes of tempering,bending, or the like in certain example instances. For example, vehiclewindshields are made up of a pair of glass substrates that are heat bentand laminated together via an adhesive layer (e.g., PVB based layer).One of the glass substrates may have a coating thereon which issubjected to the heat treatment along with the glass.

In certain situations, designers of coated articles often strive for acombination of high visible transmission, substantially neutral color,low emissivity (or emittance), and low sheet resistance (R_(s)). Highvisible transmission for example may permit coated articles to be moredesirable in applications such as vehicle windshields or the like,whereas low-emissivity (low-E) and low sheet resistance characteristicspermit such coated articles to block significant amounts of IR radiationso as to reduce for example undesirable heating of vehicle or buildinginteriors.

In applications such as vehicle windshields requiring a visibletransmission of at least 70%, or even at least 75%, the coated articlemust be bent as well as heat treated. The bending is often performed byallowing a coated glass article to sag while being heat treated in aknown manner. The heat treatment of such coated articles typicallyrequires the use of temperature(s) of at least 580 degrees C., morepreferably of at least about 600 degrees C. and often at least 620degrees C., for about 5-10 minutes or more.

Unfortunately, too much bending with heat treating in making windshieldsoften causes such coated articles to suffer damage known as mottling.Mottling defects essentially result from cracking of the coating.Mottling appears in a windshield during the bending process, and isobserved after the bending process is complete. It is detected as anoptical distortion, similar to a vertical “crack” in the windshield.Mottling defects in windshields are often roughly 5 mm long and roughly100 μm wide, and several microns deep in certain example instances. Withcertain coated articles, mottling occurs when the coated article is heatbent to a significant extent. It is believed that the mottling damageresults from high degrees of bending during heat treatment.

FIG. 1 is provided for the purpose of explaining the degree of bendingof a coated glass article such as a vehicle windshield. FIG. 1 is across sectional view of a bent vehicle windshield. Parameter “x” in FIG.1 represents the amount of bend in the windshield, and is known as acenterline convex value. The centerline convex value x is the distancebetween the apex of the interior surface of the windshield drawnstraight down to a line (see the dotted line in FIG. 1) connecting thetwo ends of the windshield. This centerline convex value x isrepresentative of the amount of bend (or depth of bend) in thewindshield; the higher the value x, the higher the amount of bend in thewindshield. FIG. 2 is a cross sectional view of a heat bent vehiclewindshield (e.g., of FIG. 1, or an embodiment herein) which includesfirst and second heat bent glass substrates 1, 40 laminated to oneanother via a polymer inclusive layer (e.g., of or including PVB or anyother suitable polymer inclusive material) 42, where the low-E (lowemissivity) coating 30 is provided on one of the substrates. While manyknown windshields are capable of withstanding bends of about 18 mm(i.e., a centerline convex value x of about 18 mm), they often cannotwithstand bending to a greater extent without suffering from fatalmottling damage.

Consider the following coated article with the below-listed layer stack,where the layers are listed in order from the glass substrate outwardly.

Glass Substrate

TiO₂

Si₃N₄

ZnO

Ag

NiCrO_(x)

SnO₂

Si₃N₄

ZnO

Ag

NiCrO_(x)

SnO₂

Si₃N₄

While the aforesaid coated article is heat treatable, it cannotwithstand significant degrees of heat bending without suffering fatalmottling damage. For example, such a coated article suffers fatalmottling damage at centerline convex values x of about 22-23 mm or more(i.e., a bend about 22-23 mm or more deep).

It will be appreciated by those skilled in the art that there sometimesexists a need for a vehicle windshield which is bent to a significantextent (e.g., bent to a centerline convex value x of at least about 24mm, sometimes at least about 26 mm, or at least 28 mm, or even at least30 or 32 mm in certain situations). Unfortunately, the coated articlediscussed above cannot be used in such applications because it cannotwithstand such high degrees of bending without suffering fatal mottlingdamage.

Additionally, consider the following coated article with thebelow-listed layer stack, where the layers are listed in order from theglass substrate outwardly (thicknesses in angstroms).

Glass Substrate Si₃N₄ 186 Å ZnAlO_(x) 107 Å Ag 107 Å NiCrO_(x) 30 Å SnO₂520 Å Si₃N₄ 131 Å ZnAlO_(x) 119 Å Ag 103 Å NiCrO_(x) 33 Å SnO₂ 120 ÅSi₃N₄ 320 Å

While the above coated article realizes satisfactory results in manyinstances, it too is subject to mottling in high bend (during HT)applications used in windshields. Again, it will be appreciated by thoseskilled in the art that there sometimes exists a need for a vehiclewindshield which is bent to a significant extent (e.g., bent to acenterline convex value x of at least about 24 mm, sometimes at leastabout 26 mm, or at least 28 mm, or even at least 30 or 32 mm in certainsituations). Unfortunately, the coated article discussed above cannot beused in such applications because it cannot withstand such high degreesof bending without suffering fatal mottling damage.

Moreover, in vehicle windshield or other applications such as ininsulating glass (IG) window units, lengthy heat treatments at hightemperatures tend to cause the aforesaid coated article to suffersignificant drops in visible transmission, significant changes incertain color value(s), and significant increases in sheet resistance(R_(s)). Thus, there is room for improvement in one or more of theserespects. Additionally, the aforesaid coated article is susceptible toscratching in certain instances, and is also sometimes characterized byhigh haze values following heat treatment in certain instances.

In view of the above, it will be apparent to those skilled in the artthat there exists a need for coated articles which are capable of one ormore of: (a) being bent to greater extents in applications such asvehicle windshields or the like, (b) being able to maintain acceptableoptical characteristics when bent to such extents, (c) realizingimproved or good thermal stability with regard to visible transmission,color, emissivity (or emittance), and/or sheet resistance (R_(s));and/or (d) realizing good mechanical durability such as scratchresistance and reduced mottling. In certain example embodiments, it maybe desired that one or more of these characteristics can be achieved.

BRIEF SUMMARY OF EXAMPLE EMBODIMENTS OF THE INVENTION

Certain example embodiments of this invention relate to a low-E coating.In certain example embodiments, the coated article may be heat treated(e.g., thermally tempered, heat bent and/or heat strengthened) in makinga vehicle windshield or the like. In certain example embodiments of thisinvention, the low-E coating includes a zinc stannate based layerprovided over a tin oxide based layer, in a central portion of the layerstack between first and second IR reflecting layers (e.g., Ag basedlayers). In certain example embodiments, the zinc stannate based layeris provided between and contacting the underlying tin oxide based layerand an overlying silicon nitride and/or silicon oxynitride based layer,so that the layer stack between the IR reflecting layers moving awayfrom the glass substrate comprises layers comprising the followingmaterials: glass . . . Ag . . . SnO/ZnSnO/SiN . . . Ag . . . . It hassurprisingly been found that this layer stack significantly reducesmottling problems upon heat treatment, thereby resulting in a moredurable coated article and/or a windshield that can be bent to a greaterdegree without suffering fatal mottling damage. Coated articlesaccording to certain example embodiments of this invention may be usedin the context of vehicle windshields (e.g., in laminated form),insulating glass (IG) window units, other types of windows, or in anyother suitable application.

In certain example embodiments of this invention, coated articles withsuch a layer stack can be heat bent to a centerline convex value “x” ofat least about 24 mm, more preferably at least about 26 mm, morepreferably at least 28 mm, even more preferably at least 30 mm, stillmore preferably at least about 32 mm, more preferably at least about 34mm, and sometimes at least about 36 mm, without suffering significant orfatal mottling damage.

In certain example embodiments of this invention, it is possible thatsuch a layer stack comprising: glass . . . Ag . . . SnO/ZnSnO/SiN . . .Ag . . . , can improve mechanical durability in applications such asvehicle windshields and/or the like.

These surprisingly results, which in certain example instances areassociated with the use of the combination layer stack portion of glass. . . Ag . . . SnO/ZnSnO/SiN . . . Ag . . . , are highly advantageoussince reduction in mottling damage, bendability and/or improved scratchresistance are typically desired features in coated articles such asvehicle windows, IG window units, and/or the like.

In certain example embodiments of this invention, there is provided amethod of making a vehicle windshield, the method comprising: having orproviding a coating on a glass substrate, the coating comprising firstand second layers comprising silver with at least the following layerstherebetween moving away from the glass substrate: a contact layer overand contacting the first layer comprising silver, a layer comprising tinoxide over at least the contact layer, a layer comprising zinc stannateover and contacting the layer comprising tin oxide, a layer comprisingsilicon nitride over at least the layer comprising zinc stannate, and alayer comprising zinc oxide over at least the layer comprising siliconnitride; and heat bending the glass substrate with the coating thereonto an extent so as to have a centerline convex value “x” of at leastabout 28 mm without experiencing significant mottling damage due to theheat bending.

In other example embodiments of this invention, there is provided acoated article comprising a coating supported by a glass substrate, thecoating comprising from the glass substrate outwardly: a layercomprising silicon nitride; a first layer comprising zinc oxide locatedover and contacting the layer comprising tin oxide; a first infrared(IR) reflecting layer located over and contacting the layer comprisingzinc oxide; a layer comprising tin oxide located over the first IRreflecting layer; a layer comprising zinc stannate located over thelayer comprising tin oxide; a layer comprising silicon nitride locatedover the layer comprising zinc stannate; a second IR reflecting layerlocated over the layer comprising silicon nitride; and at least anotherdielectric layer located over the second IR reflecting layer.

In still further example embodiments of this invention, there isprovided a method of making a coated article, the method comprising:heat treating a glass substrate with a coating thereon, the coatingcomprising first and second layers comprising silver with at least alayer comprising zinc stannate therebetween, wherein the layercomprising zinc stannate is provided between at least a layer comprisingtin oxide and a layer comprising silicon nitride, wherein the layercomprising zinc stannate is located over and contacting the layercomprising tin oxide; and heat bending the glass substrate with thecoating thereon without experiencing significant mottling damage due tothe heat bending.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating the centerline convex value(“x”) of a bent vehicle windshield or other bent coated article.

FIG. 2 is a cross sectional view of a bent vehicle windshield, of FIG.1, or of a suitable embodiment of this invention.

FIG. 3 is a cross sectional view of a coated article according to anexample embodiment of this invention.

DETAILED DESCRIPTION OF EXAMPLES OF THE INVENTION

Coated articles herein may be used in applications such as bent vehiclewindshields, other types of vehicle windows, and/or any other suitableapplication such as in an IG or monolithic window unit.

Certain example embodiments of this invention relate to a low-E coating30 used in connection with a vehicle windshield or the like. In certainexample embodiments, the coated article may be heat treated (e.g.,thermally tempered, heat bent and/or heat strengthened) in making avehicle windshield or the like. In certain example embodiments of thisinvention, the low-E coating 30 includes a zinc stannate based layer 14provided over a tin oxide based layer 13, in a central portion of thelayer stack between first and second IR reflecting layers 9 and 19(e.g., see FIG. 3). In certain example embodiments, the zinc stannatebased layer 14 is provided between and contacting the underlying tinoxide based layer 13 and an overlying silicon nitride and/or siliconoxynitride based layer 15, so that the layer stack between the IRreflecting layers 9 and 19 moving away from the glass substrate 1comprises layers comprising the following materials: glass . . . Ag . .. SnO/ZnSnO/SiN . . . Ag . . . . It is noted that zinc stannate is acombination of zinc/tin oxide. It has surprisingly been found that thislayer stack significantly reduces mottling problems upon heat treatment,thereby resulting in a more durable coated article and/or a windshieldthat can be bent to a greater degree without suffering fatal mottlingdamage. In other words, unexpectedly, it has been found that the use ofsuch a zinc stannate based layer, between tin oxide and silicon nitrideinclusive layers, results in significantly improved bendability ofcoated articles in applications such as vehicle windshields or the like.In particular, it has surprisingly been found that the provision of sucha layer stack permits a coated article to be bent to a significantlygreater extent without suffering significant or fatal mottling damage incertain example embodiments of this invention. Coated articles accordingto certain example embodiments of this invention may be used in thecontext of vehicle windshields (e.g., in laminated form), insulatingglass (IG) window units, other types of windows, or in any othersuitable application.

The second conventional coating shown above in the background sectionhas a typical layer stack containing a layer of tin oxide as the maincenter dielectric. This layer is often deposited from two tin cathodesduring a sputter-deposition process. This tin oxide undergoes acrystallization during heat treatment (e.g., as in tempering orwindshield bending), which is associated with a significant change instress of this layer moving from a strong compressive stress asdeposited to a lesser or even tensile stress after heat treatment (HT).This stress change can occur very rapidly at certain temperatures duringthe heating cycle. In contrast, it has been found that the zinc stannate(ZnSnO) based layer 14 in certain example embodiments of this invention,between layers comprising tin oxide 13 and silicon nitride 15, does notundergo the same crystallization change upon heating/bending, andremains substantially amorphous after heating during the HT. There maybe, however, a change of stress in the zinc stannate based layer withthe heating, that is less rapid than is realized with the tin oxidelayer. This change in stress occurs at a higher temperature for the zincstannate based layer 14, than for the tin oxide layer in theconventional coating. For example, this change in stress can happen atabout 400 degrees C. for the zinc stannate based layer 14, compared toat about 360 degrees C. for the central tin oxide dielectric layer inthe conventional coating. Based on experimental results, it has beenfound that use of (a) glass . . . Ag . . . SnO/ZnSnO/SiN . . . Ag . . .according to certain embodiments of this invention, instead of theconventional (b) glass . . . Ag . . . SnO/SiN . . . Ag . . . , reducesthe undesirable mottling effect. Moreover, the order of the zincstannate (ZnSnO) based layer 14 being over top of the tin oxide basedlayer 13 has been found to be particularly important as well in reducingmottling, because reversing the order of these two layers has no ornegative impact and mottling is still realized. When bent to the samebend degrees, windshields as shown in FIGS. 1-3 having the FIG. 3coating show no or little mottling, whereas windshields having thecoating shown in the background section do realize mottling.

In certain example embodiments of this invention, improved mechanicaldurability and/or reduced damage upon heat treatment can be realizedwhen thermodynamically stable silver based layers 9, 19 are deposited,and the use of the layer comprising zinc stannate 14 between layerscomprising tin oxide 13 and silicon nitride 15 is believed to aid inproviding such silver based layers with stability during heat treatmentand/or bending even though the zinc stannate need not be in directcontact with the silver in certain example embodiments of thisinvention. In other words, it has unexpectedly been found that byproviding the layer comprising zinc stannate 14 between layerscomprising tin oxide 13 and silicon nitride 15, significantly improvedbendability can be achieved.

In certain example embodiments of this invention, coated articles withsuch a layer stack can be heat bent to a centerline convex value “x” ofat least about 24 mm (e.g., see FIG. 1), more preferably at least about26 mm, more preferably at least about 28 mm, even more preferably atleast 30 mm, still more preferably at least about 32 mm, more preferablyat least about 34 mm, and sometimes at least about 36 mm, withoutsuffering significant or fatal mottling damage. In certain exampleembodiments of this invention, it is possible that the layer comprisingzinc stannate 14 between layers comprising tin oxide 13 and siliconnitride 15 can also improve mechanical durability (e.g., scratchresistance) in applications such as vehicle windshields, IG windowunits, monolithic windows, and/or the like.

These surprisingly results, which in certain example instances areassociated with the use of the combination layer stack portion of glass. . . Ag . . . SnO/ZnSnO/SiN . . . Ag . . . , are highly advantageous,since reduction in mottling damage, bendability and/or improved scratchresistance are typically desired features in coated articles such asvehicle windows, IG window units, and/or the like. In certain exampleembodiments, the dielectric zinc stannate (e.g., ZnSnO or the like)based layer 14 may include more Zn than Sn by weight. For example, thezinc stannate based layer 14 may include about 52% Zn and about 48% Sn(in addition to the oxygen) in certain example embodiments of thisinvention. Thus, for example, the zinc stannate based layer may besputter-deposited using a metal target comprising about 52% Zn and about48% Sn in certain example embodiments of this invention. Optionally, thezinc stannate based layer 14 may be doped with other metals such as Alor the like.

Optionally, the provision of an overcoat layer of or including zirconiumoxide (not shown) or the like can reduce and/or eliminate such thermalstability problems. In particular, in certain example embodiments ofthis invention, the use of a zirconium oxide inclusive overcoat layer incombination with the glass . . . Ag . . . SnO/ZnSnO/SiN . . . Ag . . .can result in a coated article which does not suffer from significantthermal stability issues (e.g., the coated article can realizeacceptable visible transmission, a* and/or b* values following heattreatment and bending).

Example advantages associated with certain example embodiments of thisinvention include a coated article which is capable of include one ormore of: (a) being bent to greater extents in applications such asvehicle windshields or the like, (b) being able to maintain acceptableoptical characteristics when bent to such extents, (c) reduced mottlingdamage upon heat treatment and bending, (d) realizing improved or goodthermal stability with regard to visible transmission, color, emissivity(or emittance), and/or sheet resistance (R_(s)); (e) realizing improvedmechanical durability. In certain example embodiments, one or more ofthese characteristics/advantages can be achieved.

In certain example embodiments of this invention, the coating includes adouble-silver stack, although this invention is not so limited in allinstances (e.g., three silver based layers can be used in certaininstances). For example, in certain example embodiments of thisinvention, heat treated and/or heat bent coated articles having multipleIR reflecting layers (e.g., two spaced apart silver based layers) arecapable of realizing a sheet resistance (R_(s)) of less than or equal to3.0 (more preferably less than or equal to 2.5, even more preferablyless than or equal to 2.1, and most preferably less than or equal to2.0). In certain example embodiments, following heat treatment and asmeasured in monolithic and/or laminated form, coated articles herein arecapable of realizing a visible transmission (Ill. C, 2 degree) of atleast about 70%, more preferably of at least about 75%, and mostpreferably of at least about 76%.

The terms “heat treatment” and “heat treating” as used herein meanheating the article to a temperature sufficient to achieve thermaltempering, heat bending, and/or heat strengthening of the glassinclusive coated article. This definition includes, for example, heatinga coated article in an oven or furnace at a temperature of least about580 degrees C., more preferably at least about 600 degrees C., for asufficient period to allow tempering, bending, and/or heatstrengthening. In certain instances, the HT may be for at least about 4or 5 minutes or more.

Bending may be performed in any suitable manner. For example, andwithout limitation, in forming a windshield including a pair of glasssubstrates, two flat glass substrates (at least one with a coatingthereon) can be placed in a bending furnace (e.g., on a bending mold) inan overlapping manner by interposing an optional lubricating powder suchas sodium hydrogen carbonate, cerite, magnesium oxide, silica, or thelike between contacting surfaces of the two glass substrates. The glasssubstrates are then heated using infrared (IR) emitting heating elementsto a processing temperature(s) near a softening point of the glass(e.g., from about 550 to 850 degrees C., more preferably from about 580to 750 degrees C.) in order to soften the overlapping glass substrates.Upon softening, the glass substrates (including any solar controlcoating such as a low-E coating thereon) are bent by their deadweight(i.e., sagging) along a shaping surface of a bending mold (not shown)into the desired curved shape appropriate for the vehicle windshieldbeing made. A press bending apparatus may optionally be used after theglass is sufficiently softened (e.g., press bending may be conducted asthe final step before cooling the glass). After being heat bent in sucha manner, the bent glass substrates (with solar control coating still onthe bent substrate) are separated from one another and a polymerinclusive interlayer sheet (e.g., PVB) is interposed therebetween. Thebent glass substrates are then laminated to one another via the polymerinclusive interlayer (e.g., PVB) in order to form the resulting vehiclewindshield.

FIG. 3 is a side cross sectional view of a coated article according toan example non-limiting embodiment of this invention. The coated articleincludes substrate 1 (e.g., clear, green, bronze, or blue-green glasssubstrate from about 1.0 to 10.0 mm thick, more preferably from about1.0 mm to 3.5 mm thick), and coating (or layer system) 30 provided onthe substrate 1 either directly or indirectly. The coating (or layersystem) 30 includes: bottom silicon nitride inclusive dielectric layer 3which may be Si₃N₄, of the Si-rich type for haze reduction, or of anyother suitable stoichiometry in different embodiments of this invention,first lower contact layer 7 (which contacts IR reflecting layer 9),first conductive and preferably metallic infrared (IR) reflecting layer9, first upper contact layer 11 (which contacts layer 9), dielectriclayer 13 (which may be deposited in one or multiple steps in differentembodiments of this invention) of or including tin oxide, dielectriclayer 14 comprising zinc stannate over and contacting the tin oxidebased layer 13, another dielectric silicon nitride inclusive layer 15which may or may not include some oxide, second lower contact layer 17(which contacts IR reflecting layer 19), second conductive andpreferably metallic IR reflecting layer 19, second upper contact layer21 (which contacts layer 19), dielectric layer 23, and silicon nitrideinclusive layer 25, and an finally optional protective dielectric layerof or including zirconium oxide or the like (not shown). The “contact”layers 7, 11, 17 and 21 each contact at least one IR reflecting layer(e.g., layer based on Ag). The aforesaid layers 2-25 make up low-E(i.e., low emissivity) coating 30 which is provided on glass or plasticsubstrate 1.

In monolithic instances, the coated article includes only one glasssubstrate 1 as illustrated in FIG. 1. However, monolithic coatedarticles herein may be used in devices such as laminated vehiclewindshields, IG window units, and the like. As shown in FIG. 2, alaminated vehicle window such as a windshield typically includes firstand second glass substrates 1 and 40 laminated to one another via apolymer based interlayer 42 (e.g., see U.S. Pat. No. 6,686,050, thedisclosure of which is incorporated herein by reference). One or both ofthese substrates of the laminate may support low-E coating 30 on aninterior surface thereof in certain example embodiments (eithersubstrate may support the low-E coating 30, although the inner substratesupports the coating in the example shown in FIG. 2). As for IG windowunits, an IG window unit may include two spaced apart substrates. Anexample IG window unit is illustrated and described, for example, inU.S. Pat. No. 6,632,491, the disclosure of which is hereby incorporatedherein by reference. An example IG window unit may include, for example,the coated glass substrate 1 shown in FIG. 3 coupled to another glasssubstrate via spacer(s), sealant(s) or the like with a gap being definedtherebetween. This gap between the substrates in IG unit embodiments mayin certain instances be filled with a gas such as argon (Ar).

Dielectric layers 3 and 15 may be of or include silicon nitride incertain embodiments of this invention. Silicon nitride layers 3 and 15may, among other things, improve heat-treatability of the coatedarticles, e.g., such as thermal tempering or the like, and may or maynot include some oxygen. The silicon nitride of layers 3 and/or 15 maybe of the stoichiometric type (i.e., Si₃N₄), or alternatively of theSi-rich type in different embodiments of this invention. For example,Si-rich silicon nitride 3 (and/or 15) combined with zinc stannate 14and/or tin oxide 13 under a silver based IR reflecting layer 19 maypermit the silver to be deposited (e.g., via sputtering or the like) ina manner which causes its sheet resistance to be lessened compared to ifcertain other material(s) were under the silver. Moreover, the presenceof free Si in a Si-rich silicon nitride inclusive layer 3 and/or 15 mayallow certain atoms such as sodium (Na) which migrate outwardly from theglass 1 during heat treatment (HT) to be more efficiently stopped by theSi-rich silicon nitride inclusive layer before they can reach the silverand damage the same.

In certain example embodiments, when Si-rich silicon nitride is used inlayer 3 and/or 15, the Si-rich silicon nitride layer as deposited may becharacterized by Si_(x)N_(y) layer(s), where x/y may be from 0.76 to1.5, more preferably from 0.8 to 1.4, still more preferably from 0.85 to1.2. Moreover, in certain example embodiments, before and/or after HTthe Si-rich Si_(x)N_(y) layer(s) may have an index of refraction “n” ofat least 2.05, more preferably of at least 2.07, and sometimes at least2.10 (e.g., 632 nm) (note: stoichiometric Si₃N₄ which may also be usedhas an index “n” of 2.02-2.04). In certain example embodiments, it hassurprisingly been found that improved thermal stability is especiallyrealizable when the Si-rich Si_(x)N_(y) layer(s) as deposited has anindex of refraction “n” of at least 2.10, more preferably of at least2.20, and most preferably from 2.2 to 2.4. Also, the Si-rich Si_(x)N_(y)layer in certain example embodiments may have an extinction coefficient“k” of at least 0.001, more preferably of at least 0.003 (note:stoichiometric Si₃N₄ has an extinction coefficient “k” of effectively0). Again, in certain example embodiments, it has surprisingly beenfound that improved thermal stability can be realized when “k” for theSi-rich Si_(x)N_(y) layer(s) is from 0.001 to 0.05 as deposited (550nm). It is noted that n and k tend to drop due to heat treatment.

Any and/or all of the silicon nitride layers discussed herein may bedoped with other materials such as stainless steel or aluminum incertain example embodiments of this invention. For example, any and/orall silicon nitride layers discussed herein may optionally include fromabout 0-15% aluminum, more preferably from about 1 to 10% aluminum, incertain example embodiments of this invention. The silicon nitride maybe deposited by sputtering a target of Si or SiAl in an atmosphereincluding at least nitrogen gas in certain embodiments of thisinvention.

Infrared (IR) reflecting layers 9 and 19 are preferably substantially orentirely metallic and/or conductive, and may comprise or consistessentially of silver (Ag), gold, or any other suitable IR reflectingmaterial. IR reflecting layers 9 and 19 help allow the coating to havelow-E and/or good solar control characteristics. The IR reflectinglayers may, however, be slightly oxidized in certain embodiments of thisinvention.

The upper contact layers 11 and 21 may be of or include nickel (Ni)oxide, chromium/chrome (Cr) oxide, or a nickel alloy oxide such asnickel chrome oxide (NiCrO_(x)), or other suitable material(s), incertain example embodiments of this invention. The use of, for example,NiCrO_(x) in these layers (11 and/or 21) allows durability to beimproved. The NiCrO_(x) of layers 11 and/or 21 may be fully oxidized incertain embodiments of this invention (i.e., fully stoichiometric), oralternatively may only be partially oxidized (i.e., sub-oxide). Incertain instances, the NiCrO_(x) layers 11 and/or 21 may be at leastabout 50% oxidized. Contact layers 11 and/or 21 (e.g., of or includingan oxide of Ni and/or Cr) may or may not be oxidation graded indifferent embodiments of this invention. Oxidation grading means thatthe degree of oxidation in the layer changes throughout the thickness ofthe layer. For example, a contact layer 11 and/or 21 may be graded so asto be less oxidized at the contact interface with the immediatelyadjacent IR reflecting layer than at a portion of the contact layer(s)further or more/most distant from the immediately adjacent IR reflectinglayer. Descriptions of various types of oxidation graded contact layersare set forth in U.S. Pat. No. 6,576,349, the disclosure of which ishereby incorporated herein by reference. Contact layers 11 and/or 21(e.g., of or including an oxide of Ni and/or Cr) may or may not becontinuous in different embodiments of this invention across the entireunderlying IR reflecting layer.

Dielectric layer 13 may be of or include tin oxide in certain exampleembodiments of this invention. However, it may be doped with certainother materials in other example embodiments, such as with Al or Zn incertain example alternative embodiments.

Lower contact layers 7 and/or 17 in certain embodiments of thisinvention are of or include zinc oxide (e.g., ZnO). The zinc oxide oflayers 7 and/or 17 may contain other materials as well such as Al (e.g.,to form ZnAlO_(x)). For example, in certain example embodiments of thisinvention, one or more of zinc oxide layers 7, 17 may be doped with fromabout 1 to 10% Al, more preferably from about 1 to 5% Al, and mostpreferably about 1 to 4% Al.

Zinc stannate based layer 14 is provided over and contacting layer 13comprising tin oxide and under and possibly contacting layer 15 of orincluding silicon nitride, in a central portion of the layer stackbetween first and second IR reflecting layers 9 and 19. As mentionedabove, it has surprisingly been found that this layer stacksignificantly reduces mottling problems upon heat treatment, therebyresulting in a more durable coated article and/or a windshield that canbe bent to a greater degree without suffering fatal mottling damage. Inother words, unexpectedly, it has been found that the use of such a zincstannate based layer, between tin oxide and silicon nitride inclusivelayers, results in significantly improved bendability of coated articlesin applications such as vehicle windshields or the like. In certainalternative embodiments, it is possible to dope the zinc stannate basedlayer 14 and/or tin oxide based layer 13 with other materials such asAl, Zn, N, or the like.

Dielectric layer 23 may be of or include tin oxide in certain exampleembodiments of this invention. However, layer 23 is optional and neednot be provided in certain example embodiments of this invention.Dielectric layer 25 may be of or include silicon nitride (e.g., Si₃N₄)or any other suitable material in certain example embodiments of thisinvention. Optionally, other layers may be provided above layer 25.Layer 25 is provided for durability purposes, and to protect theunderlying layers during heat treatment and/or environmental use. Incertain example embodiments, layer 25 may have an index of refraction(n) of from about 1.9 to 2.2, more preferably from about 1.95 to 2.05.Optionally, the provision of an overcoat layer of or including zirconiumoxide (not shown) can reduce and/or eliminate certain thermal stabilityissues.

In certain example embodiments, it has been found that good opticalproperties are achieved when the total thickness of the combination ofzinc stannate based layer 14 and tin oxide inclusive layer 13 is fromabout 430 to 650 Å, more preferably from about 460 to 600 Å, and mostpreferably from about 500 to 540 Å. In certain example embodiments, zincstannate based layer 14 and tin oxide inclusive layer 13 haveapproximately the same thickness, and do not differ in thickness fromeach other by more than about 100 Å, more preferably by no more thanabout 60 or 30 Å. Each of layers 13 and 14 is thicker than siliconnitride based layer 15 in certain example embodiments of this invention,preferably by at least about 50 Å, more preferably by at least about 75or 100 Å.

Other layer(s) below or above the illustrated coating may also beprovided. Thus, while the layer system or coating is “on” or “supportedby” substrate 1 (directly or indirectly), other layer(s) may be providedtherebetween. Thus, for example, the coating of FIG. 3 may be considered“on” and “supported by” the substrate 1 even if other layer(s) areprovided between layer 3 and substrate 1. Moreover, certain layers ofthe illustrated coating may be removed in certain embodiments, whileothers may be added between the various layers or the various layer(s)may be split with other layer(s) added between the split sections inother embodiments of this invention without departing from the overallspirit of certain embodiments of this invention.

While various thicknesses and materials may be used in layers indifferent embodiments of this invention, example thicknesses andmaterials for the respective layers on the glass substrate 1 in the FIG.3 embodiment are as follows, from the glass substrate outwardly:

Example Materials/Thicknesses; FIG. 3 Embodiment Layer Preferred MoreGlass (1-10 mm thick) Range ({acute over (Å)}) Preferred ({acute over(Å)}) Example (Å) Si_(x)N_(y) (layer 3) 40-450 Å 70-300 Å 186 ÅZnAlO_(x) (layer 7) 10-300 {acute over (Å)} 40-150 {acute over (Å)} 107Å Ag (layer 9) 50-250 {acute over (Å)} 80-120 {acute over (Å)} 107 ÅNiCrO_(x) (layer 11) 10-100 {acute over (Å)} 12-40 {acute over (Å)} 30 ÅSnO₂ (layer 13) 100-500 Å 200-320 Å 260 Å ZnSnO (layer 14) 100-500 Å200-320 Å 260 Å Si_(x)N_(y) (layer 15) 50-450 {acute over (Å)} 80-200{acute over (Å)} 131 Å ZnAlO_(x) (layer 17) 10-300 {acute over (Å)}40-150 {acute over (Å)} 119 Å Ag (layer 19) 50-250 {acute over (Å)}80-220 {acute over (Å)} 103 Å NiCrO_(x) (layer 21) 10-100 {acute over(Å)} 20-45 {acute over (Å)} 33 Å SnO₂ (layer 23) 0-750 Å 70-180 Å 120 ÅSi₃N₄ (layer 25) 10-750 {acute over (Å)} 190-400 {acute over (Å)} 320 Å

In certain example embodiments of this invention, coated articles hereinmay have the following optical and solar characteristics when measuredmonolithically (before any optional HT). The sheet resistances (R_(s))herein take into account all IR reflecting layers (e.g., silver layers9, 19).

Optical/Solar Characteristics (Monolithic; pre-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=5.0 <=4.0<=3.0 E_(n): <=0.07 <=0.04 <=0.03 T_(vis) (Ill. C 2°): >=70% >=75% >=77%

In certain example embodiments, coated articles herein may have thefollowing characteristics, measured monolithically for example, afterheat treatment (HT):

Optical/Solar Characteristics (Monolithic; post-HT) CharacteristicGeneral More Preferred Most Preferred R_(s) (ohms/sq.): <=3.0 <=2.5<=2.1 (or <=2.0) E_(n):  <=0.07  <=0.04 <=0.03 T_(vis) (Ill. C2°): >=75% >=78% >=80% Transmitted Haze: <=0.5 <=0.4 <=0.38

Moreover, in certain example laminated embodiments of this invention,coated articles herein which have been heat treated to an extentsufficient for tempering (and optionally heat bent), and which have beenlaminated (via index oil and/or a polymer inclusive interlayer) toanother glass substrate may have the following optical/solarcharacteristics.

Example Optical Characteristics (Laminated: post-HT) CharacteristicGeneral More Preferred T_(vis) (or TY)(Ill. C 2°): >=70% >=75% a*_(t)(Ill. C 2°):   −6 to +1.0  −5 to 0.0 b*_(t) (Ill. C 2°): −2.0 to +8.00.0 to 6.0 L* (Ill. C 2°): 80-95 88-95 R_(f)Y (Ill. C, 2 deg.):   1 to13%   1 to 12% a*_(f) (Ill. C, 2°): −5.0 to +2.0 −4.0 to +0.5 b*_(f)(Ill. C, 2°): −14.0 to +10.0 −10.0 to +3.5  L* (Ill. C 2°): 30-45 33-41R_(g)Y (Ill. C, 2 deg.):   1 to 12%   1 to 10% a*_(g) (Ill. C, 2°): −5.0to +3.0 −2.5 to +2.5 b*_(g) (Ill. C, 2°): −20.0 to +10.0 −15.0 to 0   L* (Ill. C 2°): 30-40 33-38 Haze(transmissive): <=0.6 <=0.5

The following examples are provided for purposes of example only, andare not intended to be limiting unless specifically claimed.

EXAMPLES

The following Example was made via sputtering on a clear glass substrate1 so as to have approximately the layer stack set forth below. Thisexample is according to an example embodiment of this invention as shownin FIG. 3. The thicknesses are in units of angstroms (Å) and areapproximations.

Layer Glass Substrate Example 1 Si_(x)N_(y) 186 ZnAlO 107 Ag 107NiCrO_(x) 30 SnO₂ 260 ZnSnO 260 Si_(x)N_(y) 131 ZnO 119 Ag 103 NiCrO_(x)33 SnO₂ 120 Si₃N₄ 320

After being sputter deposited onto the glass substrates, the Examplecoated article was heat treated in a manner sufficient for tempering andbending, and had the optical characteristics set forth in the opticaltables above. Moreover, heat bending of the coated article with thestructure of this Example shown in FIGS. 2-3 to a centerline convexvalue “x” of 30 mm did not result in any significant mottling damage.For purposes of comparison, a similar coated article except without thezinc stannate layer suffered fatal mottling damage once the bendingreached a centerline convex value “x” of about 22-23 mm. Thus, is can beseen that the provision of the layer stack according to certain exampleembodiments of this invention, with the zinc stannate based layer 14 inbetween the tin oxide based layer 13 and silicon nitride based layer 15,unexpectedly and significantly improved the bendability of the coatedarticle and reduced mottling damage.

While the invention has been described in connection with what ispresently considered to be the most practical and preferred embodiment,it is to be understood that the invention is not to be limited to thedisclosed embodiment, but on the contrary, is intended to cover variousmodifications and equivalent arrangements included within the spirit andscope of the appended claims.

1. A method of making a vehicle windshield, the method comprising:having or providing a coating on a glass substrate, the coatingcomprising first and second layers comprising silver with at least thefollowing layers therebetween moving away from the glass substrate: acontact layer over and contacting the first layer comprising silver, alayer comprising tin oxide over at least the contact layer, a layercomprising zinc stannate over and contacting the layer comprising tinoxide, a layer comprising silicon nitride over at least the layercomprising zinc stannate, and a layer comprising zinc oxide over atleast the layer comprising silicon nitride; and heat bending the glasssubstrate with the coating thereon to an extent so as to have acenterline convex value “x” of at least about 28 mm without experiencingsignificant mottling damage due to the heat bending.
 2. The method ofclaim 1, wherein said heat bending is performed so that after said heatbending the coated article has a visible transmission of at least about75% and a sheet resistance (R_(s)) of less than or equal to 3.0ohms/square.
 3. The method of claim 1, wherein the contact layercomprising an oxide of Ni and/or Cr.
 4. The method of claim 1, whereinthe layer comprising zinc oxide is over and contacting the layercomprising silicon nitride.
 5. The method of claim 1, wherein the secondlayer comprising silver is over and contacting the layer comprising zincoxide.
 6. The method of claim 1, wherein said heat bending is performedso that after said heat bending and after laminating the glass substrateto another glass substrate the coated article comprises a vehiclewindshield, and wherein the vehicle windshield as a glass sidereflective a* color of from −2.5 to +2.5, and glass side reflective b*color of from −15.0 to
 0. 7. The method of claim 1, further comprisingheat bending the glass substrate with the coating thereon to an extentso as to have a centerline convex value “x” of at least about 30 mmwithout experiencing significant mottling damage due to the heatbending.
 8. The method of claim 1, further comprising heat bending theglass substrate with the coating thereon to an extent so as to have acenterline convex value “x” of at least about 32 mm without experiencingsignificant mottling damage due to the heat bending.
 9. The method ofclaim 1, wherein the layer comprising tin oxide is located over andcontacting the contact layer.
 10. The method of claim 1, wherein thelayer comprising zinc stannate is located between and contacting thelayer comprising silicon nitride and the layer comprising tin oxide. 11.The method of claim 1, wherein the layer comprising tin oxide consistsessentially of tin oxide.
 12. The method of claim 11, wherein the layercomprising zinc stannate consists essentially of zinc stannate.
 13. Themethod of claim 1, wherein the coating further comprises another layercomprising zinc oxide located directly under and contacting the firstlayer comprising silver.
 14. The method of claim 13, wherein the coatingfurther comprises another layer comprising silicon nitride locateddirectly under and contacting the another layer comprising zinc oxide.15. The method of claim 1, wherein the coating further comprises a layercomprising an oxide of NiCr over and directly contacting the secondlayer comprising silver.
 16. The method of claim 1, wherein the coatingfurther comprises another layer comprising tin oxide and another layercomprising silicon nitride located over the second layer comprisingsilver.
 17. A method of making a coated article, the method comprising:heat treating a glass substrate with a coating thereon, the coatingcomprising first and second layers comprising silver with at least alayer comprising zinc stannate therebetween, wherein the layercomprising zinc stannate is provided between at least a layer comprisingtin oxide and a layer comprising silicon nitride, wherein the layercomprising zinc stannate is located over and contacting the layercomprising tin oxide; and heat bending the glass substrate with thecoating thereon without experiencing significant mottling damage due tothe heat bending.
 18. The method of claim 17, further comprising heatbending the glass substrate with the coating thereon to an extent so asto have a centerline convex value “x” of at least about 28 mm withoutexperiencing significant mottling damage due to the heat bending. 19.The method of claim 17, further comprising heat bending the glasssubstrate with the coating thereon to an extent so as to have acenterline convex value “x” of at least about 30 mm without experiencingsignificant mottling damage due to the heat bending.
 20. The method ofclaim 17, wherein said heat bending is performed so that after said heatbending the coated article has a visible transmission of at least about75% and a sheet resistance (R_(s)) of less than or equal to 3.0ohms/square.
 21. The method of claim 17, wherein said heat bending isperformed so that after said heat bending and after laminating the glasssubstrate to another glass substrate the coated article comprises avehicle windshield, and wherein the vehicle windshield as a glass sidereflective a* color of from −2.5 to +2.5, and glass side reflective b*color of from −15.0 to
 0. 22. The method of claim 17, wherein the layercomprising zinc stannate is located directly under and contacting thelayer comprising silicon nitride.
 23. The method of claim 17, whereinthe layer comprising tin oxide consists essentially of tin oxide, andthe layer comprising zinc stannate consists essentially of zincstannate.